In the context of anti-submarine warfare activities, in order to be able to detect submerged submarines in a given area, sonars are generally employed, in particular active sonars. In this context, the deployment of sonars from airborne platforms, airplanes or helicopters, has been proven to be especially effective, as such platforms have high mobility with respect to submarines.
Thus, maritime patrol airplanes deploy sonobuoys that are composed of acoustic sensors, and sometimes transmitters, and a VHF system acting as a relay for communication to the aircraft.
In an analogous manner, helicopters may also be used to implement sonar transmitters and receivers that are linked, by a cable, to their platform, i.e. to the helicopter. These are then referred to as “dipping sonars”. The submerged cable-linked sub-assembly is henceforth referred to as an antenna. It comprises the sonar transmitters and receivers per se, and potentially electronic equipment associated with the transmitters and receivers. It may also comprise environmental sensors.
The dipping of these antennas into the water from the platform, the control thereof once immersed and their recovery are carried out by means of a winch located inside the helicopter. In addition to antenna deployment and recovery functions, the winch cable generally conveys the sonar signals as well as the electrical power that is required for acoustic transmission and operation of the receivers. Moreover, equipment required for generating acoustic signals and processing received acoustic data is located on board the helicopter.
The increased acoustic stealth of modern submarines has necessitated an evolution of the detection techniques employed toward high-power sonars operating at low frequency. This evolution translates into an increase in the dimensions and mass of the various sub-assemblies forming the sonar. For example, for the antenna, the fact of lowering its operating frequency has tended to increase its dimensions. Antennas have, for example, been developed in which the sound wave receivers, or hydrophones, are arranged on arms that are deployed during operation. Between sonar operating phases, the arms are folded back and the antenna, wound back in by the winch to a position referred as the storage position, is stowed inside the helicopter. It is sometimes difficult to house all of the sub-assemblies of a sonar inside a helicopter. The antenna, which is generally cylindrical in order to be omnidirectional in terms of bearing and directive in terms of elevation, is suspended by the cable that bears it. The greatest vertical dimension of the sonar is restricted by the height of the antenna at which the cable attachment at the top of the antenna must be added and, at least in part, by a winch pulley whose diameter depends on the minimum radius of curvature to which the cable may be subjected. This dimension must be able to fit, in terms of height, in the helicopter.
Regarding the increase in the mass of sonar sub-assemblies, this affects the duration of missions that a carrier is able to carry out with its sonar.